Photographic emulsions having increased sensitivity to x-ray and gamma ray radiation



PHOTGGRAPHIC EMULSIONS HAVING IN- CREASED SENSITIVITY TO X-RAY ANDGAMIMA RAY RADIATION Fritz W. H. Mueller and Ernest T. Larson, Jr.,Binghamton, N.Y., assignors to General Aniline & Film Corporation, NewYork, N.Y., a corporation of Delaware No Drawing. Filed Nov. 24, 1954,Ser. No. 471,106

19 Claims. (Cl. 96-108) This invention relates to the improvement ofphotographic materials, and more particularly to the production ofsilver halide photographic emulsions of increased sensitivity to X-rays.

Cadmium salts have been used in the manufacture of photographicemulsions for recording the effects of visible light. For example,ammonia-type and neutral boil-type celerated by the use of cadmium.

Cadmium salts were also used in gelatino silver halide emulsions toaccelerate ripening and to increase the contrast for exposure to light.The activation produced by cadmium was greatest for chlorobromideemulsions containing from 25% to 30% bromide, but could no longer beobserved when the bromide content Was lowered below or raised to 50%.

The prior art dealing with the use of cadmium salts in silver halideemulsions pertained exclusively to the improvement of photographicproperties for exposures to light. No improvement in the sensitivity toX-rays and gamma rays was reported by the early investigators.

It is an object of this invention to increase the sensitivity ofphotographic emulsions to X-rays and gamma rays as used in the practiceof X-ray diifraction, medical radiography, industrial radiography,detection of nuclear radiation, and similar applications.

Other objects will be apparent from the following description.

We have discovered that the addition of very small amounts of cadmiumion to the solutions used in precipitating a silver halide emulsion hasthe effect of increasing the X-ray and gamma ray sensitivity of thefinished emulsion. The amounts of cadmium ion used range from about0.001 to 0.2 mol percent relative to the amount of silver used.Expressed in terms ofparts per million, the amounts of cadmium ion usedrange from about 10 parts to about 2000 parts per million parts ofsilverion. The concentration of cadmium based on the silver bromide content ofthe emulsion ranges from 0.007 to 1.4 milligrams of cadmium per gram ofsilver bromide. When used in the small concentrations specified above,the cadmium produces a marked decrease in the sensitivity to visiblelight, although this sensitivity loss depends somewhat on the details ofthe emulsion formulation and the intensity level of the visible light towhich the ex- Patented Aug. 30, 1960 7 can be introduced in the presenceof a colloidal carrier as a water soluble salt of cadmium such ascadmium chloride or cadmium bromide mixed with the alkali bromidesolution to which is added the silver nitrate solution to produce theformation of crystals or grains which consist primarily of silverbromide. Except for the halide salts, a water soluble cadmium salt suchas cadmium nitrate or acetate can be mixed with the silver nitratesolution which is then added to the alkali bromide solution during theemulsification step. Irrespective of the procedure wihch is used tointroduce the cadmium ion, an increase in X-ray and gamma raysensitivity is obtained, proving that the observed increase insensitivity is a result of the addition of the cadmium ion and is notdue to the particular anion used.

Without wishing to be bound by or limited to any particular theory ofthe mechanism involved in producing increased X-ray sensitivity, it isbelieved that the cadmium ion is built into the host silver halidelattice as an impurity occupying lattice sites throughout the crystalnormally occupied by silver ion, resulting in a distortion of the normallattice structure and .thereby altering the sensitivity to X rays andgamma rays.

The following examples serve to illustrate the invention, but it. is tobe understood that the invention is not to be restricted thereto.

The two solutions were first heated separately to a temperature of 68 C.and then mixed by the addition of Solution 2 to Solution l at a slowrate over a period of 1 hour, with constant agitation. Thereafter, 60grams of dry gelatin were added and the mixture was maintained at 68C.for 20 minutes, with agitation. The emulsion was then chilled, shredded,and washed until the bromide ion concentration was milligrams perkilogram of liquid emulsion. The emulsion was remelted and thenafter-ripened for 20 minutes at 60 C. Saponin was added as a spreadingagent, formaldehyde was added as a hardener, and the emulsion coatedonto a cellulose ester film base.

The speed of this emulsion, measured as th reciprocal of the exposurerequired to produce a density of 0.5 above base and fog density,relative to that of an emulsion made at the same time and in the sameway except that the cadmium was omitted, was determined for a series ofexposures to X-rays generated at 10 kilovolts, 65 kilovolts, 250kilovolts and for exposure to the gamma rays of radium. The emulsioncontaining cadmium was found to be more than 50% faster than theemulsion containing no cadmium.

Development of the exposed X-raywas carried out 3 for 7 minutes at 20 C.in an X-ray developer having the following composition;

Water to make 50.0 mls.

The two solutions were first heated separately to a temperature of 50 C.and then mixed by adding Solution 2 to Solution 1 at a rate whichallowed completion of addition within 1 minute. The emulsion obtainedwas digested for minutes at 50 C., poured into a parchment bag anddialysed at C. in order to remove the potassium nitrate. After dialysis,100 mls. of water and a small amount of saponin were added and theemulsion coated onto a fdm base which was especially subbed forpolyvinyl alcohol coatings. The X-ray and gamma ray speed of this veryfine grain emulsion was about 50% higher than the speed of a type whichhad been prepared in an identical manner except that it did not containany cadmium ions.

Example 111 Example H was repeated with the exception that thepurification by dialysis was replaced by precipitation with ammoniumsulfate, and that the precipitated particles were washed with water andremelted prior to coating.

Example IV An X-ray emulsion was made according to the followingprocedure.

Two solutions were prepared as follows:

Solution 1:

Water cc 150.0 Potassium bromide gms 60.0 Cadmium chloride gm 0.04Gelatin gms 6.0 Solution 2:

Water cc 400 Silver nitrate gms 74 The two solutions were first heatedand then mixed by adding Solution 2 to Solution 1 at a slow rate over aperiod of 1 hour, with constant agitation. Thereafter 60 grams of drygelatin were added and the mixture maintained at 68 C. for 20 minutes,with agitation. The emulsion was then chilled, shredded, and washeduntil the bromide ion Concentration was 100 milligrams per kilogram ofemulsion. The emulsion was remelted and after-ripened for 20 minutes at60 C. A surfactant and a hardener were added and the emulsion was thencoated onto a cellulose acetate support.

The speed of this emulsion, measured as the reciprocal of the exposurerequired to produce a density of 0.5 above base and fog density,relative to that of an emulsion made at the same time and in the sameway except that the cadmium was omitted, was determined for a series ofexposures to X-rays generated at 10 kilovolts, 65 kilovolts, 250kilovolts, and for exposure to the gamma rays of radium. The emulsioncontaining cadmium was found to be about 50% faster than the emulsioncontaining no cadmium.

While the present invention has been described with reference to certainpreferred procedures and uses, it is evident that the invention is notlimited thereto, that variations, may be made in the procedure describedherein and that equivalent materials may be substituted, withoutdeparting from the spirit and scope of the invention. For instance,silver bromo-iodide emulsions can be used in place of the silver bromideemulsions illustrated in the examples and it is to be understood thatthe term silver bromide as used in the appended claims is intended toembrace silver bromide emulsions in which from to of the weight of thesilver halide is silver bromide. In place of the gelatin and polyvinylalcohol illustrated in the examples, other colloidal carrier materialscan be used such as water dispersible organic esters of cellulose,polyamides, hydroxyethyl cellulose, modified polyvinyl alcohol orpartially hydrolyzed polyvinyl acetate. Special sensitizing agents whichare known to the art can be added to the emulsions to increase theirinherent speed.

In place of saponin, synthetic surfactants or wetting agents such asisopropylnaphthalene sulfonic acid can be used which aid in thepreparation of even coatings without bubble formation. Color formersfast to diffusion and capable of forming, upon development with aprimary amino developer, azometmne and quinonimine dye images, can beadded to the emulsion in which case dye images are obtained upon colordevelopment with such primary amino developer.

We claim:

1. In a process of preparing a photographic silver halide emulsion inwhich the silver halide is predominantlysilver bromide, and wherein saidprocess includes reacting a silver nitrate solution with an alkali metalhalide solution in the presence of a dissolved colloidal carriermaterial so as to form a dispersion of silver halide grains in saidcolloidal carrier material, the improvement which comprises increasingthe sensitivity of said emulsion to X-ray and gamma ray radiation bymixing said two solutions in the presence of a cadmium salt selectedfrom the group consisting of cadmium chloride, cadmium bromide, cadmiumnitrate and cadmium acetate, the concentration of the cadmium saltranging from 0.001 to 0.2 mole percent of cadmium ion per mole of silverion used in the preparation of the emulsion.

2. In a process of preparing a photographic silver bromide emulsionwhich includes mixing a silver nitrate solution with an alkali bromidesolution containing a colloidal carrier material, the improvement whichcomprises adding to at least one of said solutions prior to mixing awater soluble carmium salt selected from the group consisting of cadmiumchloride, cadmium bromide, cadmium nitrate and cadmium acetate in aconcentration ranging from 0.001 to 0.2 mole percent of cadmium ion permol of silver ion, thereby increasing the sensitivity of said emulsionto X-ray and gamma ray radiation.

3. A process according to claim 1 wherein said cadmium salt is cadmiumnitrate.

4. A process according to claim 2 wherein said cadmium salt is cadmiumnitrate.

5. A photographic emulsion prepared according to the process of claim 3.

6. A photographic emulsion prepared according to the process of claim 4.

7. A photographic emulsion prepared according to the process of claim 1.

8. A photographic emulsion prepared according to the process of claim 2.

9. A process according to claim 1 wherein said colloidal carriermaterial is gelatin.

10. A photographic material prepared according to the process of claim9.

11. A process according to claim 1, wherein said colloidal carriermaterial is polyvinyl alcohol.

12. A photographic material prepared according to the process of claim11.

13. A process according to claim 2, wherein said 001- loidal carriermaterial is gelatin.

14. A photographic material prepared according to the process of claim13.

15. A process, according to claim 2, wherein said colloidal carriermaterial is polyvinyl alcohol.

16. A photographic material prepared according to the process of claim15.

17. A process according to claim 1 wherein said cadmium salt is added tothe alkali metal halide solution.

18. A process according to claim 2 wherein said cadmium salt is added tothe alkali bromide solution.

19. A process according to claim 2 wherein said cadmium salt is cadmiumacetate, and the cadmium actate is added to the silver nitrate solution.

Wall:

UNITED STATES PATENTS Waller et al Apr. 23, 1946 Dimsdale et al. Dec.16, 1947 Staufier et al. May 27, 1952 Hewitson et a1. Nov. 18, 1952Russell Oct. 23, 1956 FOREIGN PATENTS Great Britain July 26, 1917 OTHERREFERENCES Photographic Emulsions, pages 232-234,

American Photographic Publishing Co., Boston (1929).

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No,2,950,972 August 30, 1960 Column 2, line 17, for wihch" read whichcollim'n 4, line 30, for "lysilver" read 1 y silver line 48,, for"carmium" read cadmium Signed and sealed this 4th day of April 1961.,

(SEAL) Attest: ERNEST W. SWIDER XMXXXXXQX ARTHUR w. CROCKER AttestingOflicer Acting Commissioner of Patents

1. IN A PROCESS OF PREPARING A PHOTOGRAPHIC SILVER HALIDE EMULSION INWHICH THE SILVER HALIDE IS PREDOMINANTLY SILVER BROMIDE, AND WHEREINSAID PROCESS INCLUDES REACTING A SILVER NITRATE SOLUTION WITH AN ALKALIMETAL HALIDE SOLUTION IN THE PRESENCE OF A DISSOLVED COLLOIDAL CARRIERMATERIAL SO AS TO FORM A DISPERSION OF SILVER HALIDE GRAINS IN SAIDCOLLOIDAL CARRIER MATERIAL, THE IMPROVEMENT WHICH COMPRISES INCREASINGTHE SENSITIVITY OF SAID EMULSION TO X-RAY AND GAMMA RAY RADIANTION BYMIXING SAID TWO SOLUTIONS IN THE PRESENCE OF A CADMIUM SALT SELECTEDFROM THE GROUP CONSISTING OF CADMIUM CHLORIDE, CADMIUM BROMIDE, CADMIUMNITRATE AND CADMIUM ACETATE, THE CONCENTRATION OF THE CADMIUM SALTRANGING FROM 0.001 TO 0.2 MOLE PERCENT OF CADMIUM ION PER MOLE OF SILVERION USED IN THE PREPARATION OF THE EMULSION.